<!doctype html>
<html lang="zh-CN">
<head>
    <meta charset="UTF-8">
    <meta name="viewport"
          content="width=device-width, user-scalable=no, initial-scale=1.0, maximum-scale=1.0, minimum-scale=1.0">
    <meta http-equiv="X-UA-Compatible" content="ie=edge">
    <title>Document</title>
    <link rel="stylesheet" href="css/demo1.css" media="only screen and (max-width:640px)">
    <style>
        @media screen and (min-width: 640px){
            body{
                background-color: #cccccc;
            }
        }
    </style>
</head>
<body>

</body>
</html>